The present invention relates generally to the field of ratchet drives for hand tools, and, more specifically, to an enclosed, bidirectional ratchet drive mechanism for a high-speed power hand tool, particularly such a tool of the pneumatic type.
Previously known ratcheting mechanisms for power hand tools have been mounted on the exterior of one end of a tool body in a manner which required the moving parts of the ratchet to be exposed. With the tool so constructed, dirt and debris, such as grease and metallic filings, could enter the ratchet mechanism and increase the rate at which the various parts of the device would wear down. As the parts became worn the intermeshing portions would slip and eventually the tool had to be rebuilt or discarded. The new ratchet drive mechanism described hereafter is incorporated into a power tool in a compact and almost entirely enclosed manner so that such wear due to debris does not occur. The only portions extending from the tool housing in the present ratchet drive are the drive shaft and reverse control lever.
Other known ratchet mechanisms are useful for turning a part only in one direction. Thus any particular job may require two separate tools for alternatively rotating a part clockwise or counterclockwise. The mechanism of the present invention overcomes this problem by permitting bidirectional ratcheting with a single tool. Furthermore, this bidirectional ratcheting mechanism is incorporated into the housing of a standard size tool, so that no extra bulk is involved to complicate or otherwise impair performing a particular job. Furthermore, this change in tool operational direction can be accomplished with only one hand (indeed with only one finger) while the tool motor is running at speeds up to those in the general range of 20,000 to 25,000 rpm, enabling the user to reverse direction without removing the tool from the fastener, thus greatly increasing user efficiency.
A further drawback of some known ratcheting tools is inherent weakness and a high rate of tool breakdown due to breakage of the teeth of the ratchet drive. This is often caused by a pawl of the mechanism having only one tooth engaging a single tooth of the drive gear at any one time. Such breakage necessarily leads to a high rate of lost work hours and other costs associated with tool repair and replacement.
The present ratchet drive mechanism overcomes this historical problem by incorporating a greater number of engaging teeth, to increase the surface area carrying the turning force. Also, a drive angle is created by positioning the toothed pawl surfaces tangentially relative to the gear, which causes a positive mesh in the output gear so that the intermeshing pawls and output gear have a tendency to dig in and stay in tight mesh when driving. By thus avoiding slippage, wear of the parts is greatly reduced.
The new ratchet mechanism is entirely different from known arrangements in using oppositely-disposed, spring-biased drive pawls which have inner portions pivotally connected to a yoke shaped drive link which is driven in conventional manner by a crank having a cylindrical surface.
The driving arrangement is stronger in the new ratchet device because the thrust is carried along the length of the drive pawls, and greater numbers of teeth are in engagement at any given time. The driving relationship is such that two teeth are advanced per revolution of the drive motor shaft. This arrangement enhances drive speed without compromising torque and the output shaft can be driven at higher speeds (up to or greater than 200 rpm) than in prior constructions.
Accordingly, it is among the goals of the present invention to provide an enclosed, bidirectionally operable ratchet drive for a hand tool of the power type which ratchet drive is reasonably inexpensive to manufacture and is extremely facile to operate by anyone with even limited experience in use of power tools.
It is further among the goals of the present invention, having the features indicated, that the new ratchet drive be compact and structured so as to be capable of being incorporated within the housing of a power tool, such as a pneumatic hand tool of known size and shape, for most convenient and familiar use, and which ratchet mechanism is constructed so as to provide exceptional wear and longevity of its parts so as to lead to decreased costs associated with use of the ratcheting power tool in which the mechanism is incorporated.
Accordingly, in keeping with the above-mentioned goals, the present invention is, briefly, a ratchet drive mechanism substantially completely enclosed within the housing of a hand tool. The ratchet drive mechanism includes a drive link having a first end and a second end, the first end being disposed rearwardly within the tool housing and being adapted to engage a movement-imparting element of the hand tool and the second end being disposed forwardly within the tool housing and being adapted to movably engage at least one pawl. The at least one pawl has a first end and a second end and extends continuously therebetween and has an angle substantially centrally along the length thereof to form an elbow. The at least one pawl is movably connected to the second end of the drive link at the elbow of the at least one pawl. The mechanism also includes a drive gear with a drive shaft extending axially therefrom. The drive gear is mounted within a forward end of the housing of the hand tool with the drive shaft disposed transversely relative to a longitudinal axis of the hand tool and extending beyond the confines of the tool housing for interengagement of an item to be turned.
Other goals and advantages of the invention will be in part apparent and in part pointed out hereinbelow.